In modern oil and gas production it is desirable to position in a well devices that require a source of electrical power. Energy consuming devices may be employed downhole to perform a variety of tasks. For example, sensors may be positioned within a casing for monitoring fluid flow pressure, temperature, flow rates, and to characterize the fluid content of the flow. Other sensing devices can be useful to measure fluid viscosity and density.
With the advent of reservoir management techniques, sophisticated monitoring and valve systems have been integrated into wellbore tubing. This allows portions of a subterranean formation to be open to producing oil/gas up the wellbore, while at the same time other portions of the formation are sealed to avoid production into the wellbore. This may be accomplished by controlling downhole valves. To achieve maximum reservoir performance, it may be necessary to flow from only selected portions of the reservoir at a given time. Subterranean flow monitors and flow control systems may require an external power source to activate such valves during the life of a wellbore.
Modern subsea wells may be drilled to depths of as much as 20,000 feet or more, extending from the mud line on the ocean floor downward to the hydrocarbon producing formation. Such wells may utilize downhole valves that must be activated to open or close various portions of the reservoir to production. The determination of when valves should be open or closed may depend upon the character of the fluid being produced by the formation over the life of the well. Such wells may have a life of 20-25 years or more. Downhole sensors may be employed to determine when the wellbore conditions require the opening or closing of such valves, based in part on temperature, pressure, or content of the fluids produced at a given time during the productive life of a well.
In the past, it has been common to deploy electrical conductive cables for miles into a reservoir down to a completion string near the bottom of the well. Such electrical conductive cables fail for a variety of reasons, which may require expensive and time consuming workover operations to repair the cables. Such cables are very expensive and heavy, and require substantial expertise and care to deploy downhole. Workover operations to repair damaged cables may require several weeks of effort, and may cost as much as 22 million dollars.
There is a need in the industry for an apparatus and system for producing downhole power that can be installed for long term use in a well. The apparatus and system needs to be capable of supplying downhole power in the relatively harsh wellbore environment without the need to run electrical conductive cables the entire length of the well. A device that can generate or supply a steady source of power deep within a reservoir for long periods of time without removal from a well and without requiring electrical conductive cable connections from the power source to the surface would be highly desirable. A downhole power source that can supply a steady and long term source of power to sensors, valves or other wellbore devices is needed.